Crawler Mafia UnderDrive Mod

[rock hard]

Ok,I figure that this probably needs to be in its own thread,instead of just getting lost within the pages of a build thread.


This is the current underdrive I'm using,and I'm laying out how I did it here.
So you have something new to ponder upon.


The overdrive was not my secret to tell,but this is all mine,and it works.I know that undoubtably some of you will try this on your own.As a result I will be making little to no money from my creation.

But you know what,there is more to it than money,its about sharing tech info about something we all enjoy.

I figure that some of you won't want to deal with the hassle of this mod,so instead just send me a pm

So here you go,everyone has been wanting underdrive

My gift to you,a template to do it yourself.

Crawler Mafia Underdrive Mod

[rock hard]

Step 1

I start with a losi comp crawler 12t pinion,(Losi4112)I cut the pinion down in size 1st.

Then I cut a grove in the bottom of the pinion so it will seat on the output shaft.

This is very tedious,mainly cuz its so small its hard to work with. I can cut it down in size fairly fast.

But when making the groove,I have to really take my time. I make multiple light passes and check it every couple of passes.

The groove has be very close to perfect,the depth,width and being flat and centered are the most important part of the mod.

If I cut to much,that pinion and the money paid for it are lost.

When I'm done it looks like this

[rock hard]

Step 2

Once the pinion is cut,I can install it.
Now during the cutting process,I will have already installed the pinion multiple times to check its fit as I cut.

To install you will need a 2mm pan head screw like this.



The reason it has to be a pan head is the bore of the pinion. The bore is a larger diam. than the screw.
The pan head keeps the pinion centered,a different type of head will not keep the pinion centered.

Also the pan head has more clearance,if you use a different head screw,you will have to drill/counter sink it into the pinion.

This is what it looks like installed.

The output shaft will stick out a little more than it used to from the axle.This didnt affect my drive shafts at all.
I run ped shafts,I doubt if it will affect mip either,though havent checked as I dont own any.





Now I want you to look at where the bearings should rest,notice that the 2 sides are different.

[rock hard]

Step 3

moding the case

In order for me to get the gears to have a good contact area,I had to shim the ring gear over.

Since the pinion is smaller,the gears wouldnt make contact,I have grooved the axle housing to allow the bearing set further over.

By doing this I can shim the ring gear over to get my gears to contact.

This is no where near as tedious as cutting the pinion,but it is possible to cut to much.
If you do then the bearing will not seat properly.
So again I make multiple light passes,checking my work every couple of passes.

when its done,you have to actually bolt the axle together to really check.
It may seem to be a good fit,then when you put the housing together it may still look good.

But when you tighten down if its to tight,or not right it wont turn freely.






Notice the washer,this is my shim,the bearing is only resting on 1/2 of the locker
but is fully rested within the axle. I was worried about the plastic locker being suitable.
I know the alum lockers are fine,but I was worried the plastic locker may fail with the shift of pressure.

if you have it done right,there is no problem,I have been driving this truck with this locker and no signes of fatigue.

[rock hard]

step 4

bolt it up and test

Ok I cant call this gear full proof yet.I have had many stumbles along the way.

The 1st material/pinions I used all failed,the design worked,but the pinion wasnt of a worthy material.

This pinion is of a stronger material,the teeth are holding up well and they show very little wear.

I can't say how long the gear will last,its really still experamental,but I know its working
like a champ for me. Not just turning radious,but steep climbs and off camber are much easier now.

The only down side of running over and underdrive is the truck will load up the suspension when
you are reversing. A small reverse is no worries,a longer reverse on flat ground is no worries.

But reversing up a steep incline takes some getting used to.



Well now you have alot to consider.
And you can see the work I put into it,if your inclined to tackle it yourself
I hope this gives you the info needed to tackle the task succesfully.
But if you would rather not tackle it,pm me and I'll gladly do it for you.

Underdrive pics again

[neiloid1]

Nice work and a great thread. You've got some great mods going into your build

Thanks for sharing and letting us know what you are up to.

[ol' gravy leg]

Nice write up. Are you running the overdrive up front in conjunction with the underdrive?

[rock hard]

Originally Posted by ol' gravy leg

Nice write up. Are you running the overdrive up front in conjunction with the underdrive?

IMO the overdrive is a must,first off its to easy and cheap not to do it.

However,I have to admit,I plan to work on a 16t overdrive

[Raceaholic]

Nice job! This is why I love crawling. We share info with each other. Help each other out. And cheer for each other to do good on a course. Many great ideas are kept secret. Thank you Paul for sharing this mod. Paul does a great job. Just pm him and let him do the work for you. He has put alot of time into it. THANK YOU!!!!

[rockslyder]

First of all great write up, and thanks for the 411 on this. Do you think using a 13 or 14 pinion would be better for reverseing and mod a little easer (maybe less shimmin) just seems like a big difference between 16 front and 12 rear. Did I say awsome mod work

[EGRESSor]

looks like a motor pinion

or is it beveled?

[toytech93]

great idea ! When there is a stronger bulletproof version, I'll be ready to purchase one.

[rock hard]

Originally Posted by rockslyder

First of all great write up, and thanks for the 411 on this. Do you think using a 13 or 14 pinion would be better for reverseing and mod a little easer (maybe less shimmin) just seems like a big difference between 16 front and 12 rear. Did I say awsome mod work

The stock pinions are 14t

The overdrive mod using a traxxas mini revo pinion is a 15t

With 15 up front and 13t in the rear was good,but I like the 12t better.

I'm going to eventually have 16t up front
with a 12t in the rear. This will alllow me to run a larger diam. tires in the rear and still have a larger rollout on the front.

You can use a 13t pinion,but with this set up you still need it shimmed.

[rock hard]

Originally Posted by EGRESSor

looks like a motor pinion

or is it beveled?

Yep,and no its not beveled.

I used a bully 12t pinion and its great and its steel
But the new ones dont have the beveled edge like the old ones.

The teeth on the ring gear grow as the get farther from center(I'm sure you know this)
The teeth on the bully pinion do also,and the mesh is good.
But it does me no good if I cany get the pinions.

Now there are plenty of pinions that have a beveled edge.
But I dont like the material used.
I have tried many pinons,I always buy 2 to test with.
And its usually 25-30 bucks each time.

I found a sweet pinion that I think is gonna be the ticket.

But I dont have it in my hands yet
I will have to mod it,and run the snot out of it before I'm ready to
put it out there.

But the pinioon is hardened STEEL and BEVELED
I dont have a crystal ball though,I could say I'll have them ready by end of feb. But that would be a lie,I have no idea till a get them and get my first few batteries on em.

[rock hard]

Originally Posted by toytech93

great idea ! When there is a stronger bulletproof version, I'll be ready to purchase one.

I was really hoping to have it by now,the problem is the materials the pinions are made of.

Saying the new pinion I have such high hopes in actually works.

I see no reason why I dont have them ready to ship by end of march
That gives me Plenty of time to test.

[Jslick]

Can't wait to give this a try when it is ready. Great thinking

[rock hard]

Originally Posted by Jslick

Can't wait to give this a try when it is ready. Great thinking

But the mod above works like a champ.If you do it yourself your only out about $20
The shiming of the ring gear isnt permanent,you can always recenter it for the stock gear,or a futur drop in underdrive.
So there is no reason not to have underdrive for your next competition.
The mod is cheap,its not really easy,but I did the trail and error for ya

[rock hard]

Originally Posted by EGRESSor

looks like a motor pinion

or is it beveled?

This is the 1st steel pinion that looked to have promis to be a direct drop in.
Although I would sell it with a output shaft aswell



Problem is the 12t are now made with straight teeth.
Now there is some alum heli gears very simulare to this,but I feel the pinion needs to be steel.
I'm not wasting my time and money,or putting much trust on an alum pinion.


We are putting up our tree tomorrow

But tomorrow or monday I'll be posting pics/instructions,
on how to do the mod using this style pinion.

Although I have choosen against this pinion,it was not cuz its weak,its hard to find
If you happen to have some of these pinions laying around
You can put them to a better use.

Now Mctwist is using a hardened aluminum heli pinion with a simulare shape

I have bee searching for steel heli pinions. I have located some that
are hardened steel,and they look good.(revco hard one)
I have also been turned on to some other steel pinions by Mctwist
They too look to have some promis.(rhino)
But I have found that I dont always get whats actually pictured.

Also the 65-1 super bully pinion in 12t may work like a dream
If anyone has a 65-1 12t bully pinion pm me

Rc4wd is and has been out of stock and I would really
like to try this pinion sooner rather than later

[fordwheeler]

rock hard, very nice work, your dedication to the 1.9 class is much appreciated

btw I got my 17t in....very impressive....its official I joined the mob

[EGRESSor]

there are some Hyperion pinions that are beveled at the end , but the have the set screw in the beveled area
and i have some 10t bevelgears from duratrax http://www3.towerhobbies.com/cgi-bin...?&I=LXLFT2&P=7
they may work with the stock ring and some grinding
or with the duratrax ring gear (27T) and another spool http://www3.towerhobbies.com/cgi-bin...?&I=LXLFR5&P=7